Pulse shot flow regulator and pulse shot flow regulating method

ABSTRACT

A flow controller and a flow controlling method are adapted to be released from conventional restrictions by using a novel type called a pulse shot type. A pulse shot (opening/closing operation of a first cutoff valve ( 12 ) and, after that, opening/closing operation of a second cutoff valve ( 17 )) is repeated. Simultaneously, a volume flow Q of process gas exhausted from the second cutoff valve ( 17 ) per unit time on the basis of after-filling pressure and after-exhaust pressure of the process gas in a gas filling capacity ( 13 ) measure by a pressure sensor ( 14 ). Furthermore, a mode of the pulse shot is changed to control the volume flow Q of the process gas exhausted from the second cutoff valve ( 17 ) per unit time.

TECHNICAL FIELD

[0001] The present invention relates to a pulse shot type flowcontroller and a pulse shot type flow controlling method for controllinga volume flow of gas.

BACKGROUND TECHNIQUE

[0002] Hitherto, in a gas supply system of a semiconductor manufacturingapparatus or the like, to control a flow rate of gas, for example, athermal-type mass flow controller, a sonic-type flow controller, aCoriolis-type flow controller, an impeller-type flow controller, anultrasonic-type flow controller, a Karman's vortex type flow controller,or the like is used.

[0003] To control the flow rate of gas by using any of them, however,there are many restrictions such as (1) necessity of forcefulsuppression of a turbulent flow of gas, (2) necessity of providing ameasurement device in some midpoint of a channel of the gas, and (3)necessity of regulation of pressure of the gas.

[0004] The present invention relates to, therefore, a flow controllerand a flow controlling method achieved to solve the problem and itsobject is to release the flow controller and the flow controlling methodfrom the conventional restrictions by using a novel type called a pulseshot type.

DISCLOSURE OF THE INVENTION

[0005] The present invention has an object to provide a flow controllerand a flow controlling method adapted to solve the problem and bereleased from the conventional restrictions by using a novel type calleda pulse shot type.

[0006] A pulse shot type flow controller according to the inventionachieved to solve the problem includes: a first cutoff valve connectedto a gas source; a second cutoff valve connected to the first cutoffvalve; a gas filling capacity between the first and second cutoffvalves; and a pressure sensor for measuring pressure in the gas fillingcapacity, wherein a pulse shot of performing opening/closing operationof the first cutoff valve and, after that, performing opening/closingoperation of the second cutoff valve is repeated, and volume flow of agas exhausted from the second cutoff valve is calculated on the basis ofan after-filling pressure/an after-exhaust pressure of the gas fillingcapacity measured by the pressure sensor while controlling the volumeflow of the gas exhausted from the second cutoff valve by changing themode of the pulse shot.

[0007] In the pulse shot type flow controller according to the presentinvention, preferably, the volume flow of the gas exhausted from thesecond cutoff value is calculated by calculating volume of the gasexhausted from the second cutoff valve every the pulse shot andintegrating the volumes.

[0008] In the pulse shot type flow controller according to the presentinvention, preferably, the volume flow of the gas exhausted from thesecond cutoff valve is calculated on the basis of a predetermined cycleof repeatedly making the pulse shot.

[0009] In the pulse shot type flow controller according to the presentinvention, preferably, the mode of the pulse shot is changed by changingthe predetermined cycle of repeatedly making the pulse shot.

[0010] In the pulse shot type flow controller according to the presentinvention, preferably, the mode of the pulse shot is changed by changingopening operation duration of the first cutoff valve or the secondcutoff valve.

[0011] In the pulse shot type flow controller according to the presentinvention, preferably, the controller further comprises a temperaturesensor for measuring temperature of the gas filling capacity, and thevolume flow of the gas exhausted from the second cutoff valve iscalculated also on the basis of the temperature of the gas fillingvolume measured by the temperature sensor.

[0012] In the pulse shot type flow controller according to the presentinvention, preferably, an after-filling estimated pressure in a heatequilibrium state after filling is obtained on the basis of a changerate of pressure accompanying an adiabatic change in a period (at thetime of filling) since the opening/closing operation of the first cutoffvalve is performed until the opening/closing operation of the secondcutoff valve is performed, the after-filling estimated pressure is usedas the after-filling pressure, an after-exhaust estimated pressure in aheat equilibrium state after exhaust is obtained on the basis of achange rate of pressure accompanying an adiabatic change in a period (atthe time of exhaust) since the opening/closing operation of the secondcutoff valve is performed until the opening/closing operation of thefirst cutoff valve is performed, and the after-exhaust estimatedpressure is used as the after-exhaust pressure.

[0013] In the pulse shot type flow controller according to the presentinvention, preferably, the first cutoff valve is closed when thepressure of the gas filling capacity measured by the pressure sensorbecomes a predetermined value or larger.

[0014] In the pulse shot type flow controller according to the presentinvention, preferably, the controller is used for a semiconductormanufacturing apparatus.

[0015] Alternatively, a pulse shot type flow controlling method made tosolve the above problems is characterized by comprising: a first cutoffvalve connected to a gas source; a second cutoff valve connected to thefirst cutoff valve; a gas filling capacity between the first and secondcutoff valves; and a pressure sensor for measuring pressure in the gasfilling capacity, wherein a pulse shot of performing opening/closingoperation of the first cutoff valve and, after that, performingopening/closing operation of the second cutoff valve is repeated, andvolume flow of a gas exhausted from the second cutoff valve iscalculated on the basis of an after-filling pressure/an after-exhaustpressure of the gas filling capacity measured by the pressure sensor,while controlling the volume flow of the gas exhausted from the secondcutoff valve by changing the mode of the pulse shot.

[0016] In the pulse shot type flow controlling method according thepresent invention, preferably, the volume flow of the gas exhausted fromthe second cutoff value is calculated by calculating volume of the gasexhausted from the second cutoff valve every the pulse shot andintegrating the volumes.

[0017] In the pulse shot type flow controlling method according to thepresent invention, preferably, the volume flow of the gas exhausted fromthe second cutoff valve is calculated on the basis of a predeterminedcycle of repeatedly making the pulse shot.

[0018] In the pulse shot type flow controlling method according to thepresent invention, preferably, the mode of the pulse shot is changed bychanging the predetermined cycle of repeatedly making the pulse shot.

[0019] In the pulse shot type flow controlling method according to thepresent invention, preferably, the mode of the pulse shot is changed bychanging opening operation duration of the first cutoff valve or thesecond cutoff valve.

[0020] In the pulse shot type flow controlling method according to thepresent invention, preferably, the method further comprises atemperature sensor for measuring temperature of the gas fillingcapacity, and the volume flow of the gas exhausted from the secondcutoff valve is calculated also on the basis of the temperature of thegas filling volume measured by the temperature sensor.

[0021] In the pulse shot type flow controlling method according to thepresent invention, preferably, an after-filling estimated pressure in aheat equilibrium state after filling is obtained on the basis of achange rate of pressure accompanying an adiabatic change in a period (atthe time of filling) since the opening/closing operation of the firstcutoff valve is performed until the opening/closing operation of thesecond cutoff valve is performed, the after-filling estimated pressureis used as the after-filling pressure, an after-exhaust estimatedpressure in a heat equilibrium state after exhaust is obtained on thebasis of a change rate of pressure accompanying an adiabatic change in aperiod (at the time of exhaust) since the opening/closing operation ofthe second cutoff valve is performed until the opening/closing operationof the first cutoff valve is performed, and the after-exhaust estimatedpressure is used as the after-exhaust pressure.

[0022] In the pulse shot type flow controlling method according to thepresent invention, preferably, the first cutoff valve is closed when thepressure of the gas filling capacity measured by the pressure sensorbecomes a predetermined value or larger.

[0023] In the pulse shot type flow controlling method according to thepresent invention, preferably, the method is used for a semiconductormanufacturing apparatus.

[0024] The pulse shot type flow controller and the pulse shot type flowcontrolling method of the invention having such characteristics controlsthe volume flow of gas by using a novel type called a pulse shot typedescribed hereinbelow.

[0025] When first and second cutoff valves are in a closed state, apulse shot of performing opening/closing operation of the first cutoffvalve and, after that, performing opening/closing operation of thesecond cutoff valve is made once. The pressure in gas filling capacitybetween the first and second cutoff valves increases by the openingoperation of the first cutoff valve and decreases by the openingoperation of the second cutoff valve. Therefore, when a pressure afterfilling the gas filling capacity is Pi_(fill), a pressure afterexhausting the gas filling capacity is Pi_(redu), and the volume of thegas exhausted from the second cutoff valve is Qi in an i-th pulse shot,the volume Qi of the process gas exhausted from the second cutoff valveby the pulse shot of the i-th time is obtained by conversion inatmospheric pressure by the following equation (1).

Qi=V(Pi _(fill) −Pi _(redu))/1.0332*α  Equation (1)

[0026] where “V” denotes the capacity of the gas filling capacity and“α” indicates a correction factor (a correction term for a variationwhich is caused by flow characteristics of the first and second cutoffvalves).

[0027] In the pulse shot type flow controller and the pulse shot typeflow controlling method of the invention, since the pulse shot isrepeated, for example, the volume flow Q(i, j) of gas exhausted from thesecond cutoff valve by the i-th to j-th pulse shots is obtained by thefollowing equation (2).

Q(i,j)=Qi+Qi+1+ . . . +Qj−1+Qj   Equation (2)

[0028] In the case where the pulse shot repeats in predetermined cyclesF, when an inverse number of the predetermined cycle F is set as r(times/second), for example, a volume flow Q(i+1, i+r) of the processgas exhausted from the second cutoff valve for one second from the(i+1)th pulse shot can be obtained by the following equation (3).

Q(i+1, i+r)=Qi+1+Qi+2+ . . . +Qi+r−1+Qi+r   Equation (3)

[0029] When volumes Qi+1, Qi+2, . . . , Qi+r−1, and Qi+r of the gasexhausted from the second cutoff valve by the pulse shots are equal toeach other, for example, the following equation (4) is obtained bysimplifying the equation (3).

Q(i+1, i+r)=r×Qi+1   Equation (4)

[0030] Further, by applying the idea of the equation (4), the volumeflow Q(S) of the gas exhausted from the second cutoff valve of S secondsfrom the (i+1)th pulse shot can be obtained by the following equation(5).

Q(S)=S×Q(i+1, i+r)   Equation (5)

[0031] In the equation (5), Q(i+1, i+r) in the equation (3) or Q(i+1,i+r) in the equation (4) may be used.

[0032] According to the equations (1) to (5), by changing the mode ofthe pulse shot, the volume flow Q of gas exhausted from the secondcutoff valve can be controlled.

[0033] This point will be concretely described. For example, in the casewhere the pulse shot is repeated in predetermined cycles F, when thepredetermined cycle F of repeating the pulse shot is changed, theinverse number r (times/second) of the predetermined cycle F alsochanges. Consequently, the volume flow Q(i+1, i+r) of the gas exhaustedfrom the second cutoff valve for one second immediately after the i-thpulse shot can be controlled. Moreover, the volume flow Q of the gasexhausted from the second cutoff valve can be controlled.

[0034] According to the equation (1), the volume Qi of the gas exhaustedfrom the second cutoff valve by the i-th pulse shot is influenced by thepressure Pi_(fill) after filling of the gas filling capacity and thepressure Pi_(redu) after exhaust of the gas filling capacity. Withrespect to the point, there is a case that the pressure Pi_(fill) afterfilling of the gas filling capacity can be changed by changing openingoperation duration of the first cutoff valve. There is a case that thepressure Pi_(redu) after exhaust of the gas filling capacity can bechanged by changing opening operation duration of the second cutoffvalve. Consequently, by changing the opening operation duration of thefirst cutoff valve or the opening operation duration of the secondcutoff valve, the volume Qi of the gas exhausted from the second cutoffvalve by the i-th pulse shot can be controlled and, moreover, the volumeflow Q of the gas exhausted from the second cutoff valve can becontrolled.

[0035] When the temperature of the gas is considered in the equation(1), the volume Qi of the gas exhausted from the second cutoff valve bythe i-th pulse shot by 20° C. conversion is the value obtained by thefollowing equation (6).

Qi(T=20)=Qi×293/(Ti+273)   Equation (6)

[0036] where “Ti” denotes the temperature (° C.) of the gas fillingcapacity in the i-th pulse shot. “Qi (T=20)” is a value obtained byperforming 20° C. conversion on the volume Qi of the gas exhausted fromthe second cutoff valve by the i-th pulse shot.

[0037] In the pulse shot type flow controller and the pulse shot typeflow controlling method of the invention, the novel type called thepulse shot type is used, that is, the pulse shot of performing theopening/closing operation of the first cutoff valve and, after that,performing the opening/closing operation of the second cutoff valve isrepeated, the volume flow of the gas exhausted from the second cutoffvalve is calculated on the basis of the after-filling pressure andafter-exhaust pressure of the gas filling capacity measured by thepressure sensor and, further, the mode of the pulse shot is changed,thereby controlling the volume flow of the gas exhausted from the secondcutoff valve. Therefore, (1) there is no influence of a turbulent flowof the gas and a device such as a laminar flow tube for forcefullysuppressing turbulent flow of the gas becomes unnecessary. (2) Itbecomes unnecessary to interpose a measurement device such as a tubulein a channel of the gas. (3) The pressure of the gas is not regulated, adevice such as a regulator becomes unnecessary, and the componentsbecome simpler. In such a manner, the pulse shot type flow controllercan be released from the conventional restrictions.

[0038] In a semiconductor manufacturing apparatus, corrosive gas isused, gas replacement is performed, and a cutoff valve is often used forswitching a gas channel or the like. By using the pulse shot type flowcontroller and the pulse shot type flow controlling method for asemiconductor manufacturing apparatus, (4) since a measurement devicesuch as a tubule is not used, abnormality such as clogging caused bycorrosion does not occur. (5) Since there is no dead volume, gasreplacement can be executed with reliability. (6) By using the first andsecond cutoff valves for switching a gas channel, the number of cutoffvalves used for switching a gas channel or the like can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a diagram showing a general outline of a pulse shot typeflow controller of the invention;

[0040]FIG. 2 is a diagram showing an example of the relation betweenopening/closing operations of first and second cutoff valves undercertain conditions in pulse shots of the pulse shot type flow controllerof the invention and pressure waveform of process gas in gas fillingcapacity;

[0041]FIG. 3 is a diagram showing an example of pressure waveform ofprocess gas in the gas filling capacity of one second under certainconditions in the pulse shot type flow controller of the invention;

[0042]FIG. 4 is a diagram showing a configuration example of the gasfilling capacity in the pulse shot type flow controller of theinvention;

[0043]FIG. 5 is a diagram serving as a flowchart and a block diagram ofthe pulse shot type flow controller of the invention;

[0044]FIG. 6 is a diagram showing an example of the relation between thevolume flow of process gas exhausted by the second cutoff valve and theduty ratio of the second cutoff valve under certain conditions in thepulse shot type flow controller of the invention;

[0045]FIG. 7 is a diagram showing a general outline of the pulse shottype flow controller of the invention;

[0046]FIG. 8 is a diagram showing an example of the relation betweenopening/closing operations of the first and second cutoff valves in thecase of making pulse shots at high frequency and pressure waveform ofprocess gas in the gas filling capacity in the pulse shot type flowcontroller of the invention;

[0047]FIG. 9 is a diagram for explaining a method of calculating a timeconstant at the time of filling in the case of performing pulse shots athigh frequency in the pulse shot type flow controller of the invention;

[0048]FIG. 10 is a diagram for explaining a method of calculating a timeconstant at the time of exhaust in the case of performing pulse shots athigh frequency in the pulse shot type flow controller of the invention;

[0049]FIG. 11 is a diagram for explaining a method of calculating anafter-filling estimated pressure and an after-exhaust estimated pressurein the case of making pulse shots at high frequency in the pulse shottype flow controller of the invention;

[0050]FIG. 12 is a diagram showing waveform of pressure in the gasfilling capacity at the time of passing N₂ gas and Ar gas by performingpulse shots at high frequency in the pulse shot type flow controller ofthe invention;

[0051]FIG. 13 is a diagram showing values of various data calculated atthe time of filling when volume flow Q is calculated in consideration ofa temperature change accompanying an adiabatic change in the case ofperforming pulse shots at high frequency in the pulse shot type flowcontroller of the invention;

[0052]FIG. 14 is a diagram showing values of various data calculated atthe time of exhaust when the volume flow Q is calculated inconsideration of a temperature change accompanying an adiabatic changein the case of performing pulse shots at high frequency in the pulseshot type flow controller of the invention;

[0053]FIG. 15 is a diagram showing various data and calculation valueswhich are necessary at the time of calculating the volume flow Q inconsideration of a temperature change accompanying an adiabatic changein the case of performing pulse shots at high frequency in the pulseshot type flow controller of the invention; and

[0054]FIG. 16 is a diagram showing various data and calculation valueswhich are necessary at the time of calculating the volume flow Q withoutconsidering a temperature change accompanying an adiabatic change in thecase of performing pulse shots at high frequency in the pulse shot typeflow controller of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0055] Embodiments of the invention will be described hereinbelow withreference to the drawings. FIG. 1 shows a general outline of a pulseshot type flow controller 1. The pulse shot type flow controller 1 isconstructed of a manual valve 11, a first cutoff valve 12, a gas fillingcapacity 13, a pressure sensor 14, a temperature sensor 15, a secondcutoff valve 17, a controller 19, and the like. The first cutoff valve12, pressure sensor 14, temperature sensor 15, and second cutoff valve17 are connected to the controller 19. Therefore, each of theopening/closing operation of the first cutoff valve 12 and theopening/closing operation of the second cutoff valve 17 can becontrolled by the controller 19. The pressure sensor 14 is provided forthe gas filling capacity 13 to convert pressure in the gas fillingcapacity 13 to an electric signal. Further, the temperature sensor 15 isprovided for the gas filling capacity 13 to convert the temperature inthe gas filling capacity 13 to an electric signal. Therefore, thecontroller 19 can detect the pressure and temperature in the gas fillingcapacity 13 via the pressure sensor 14 and the temperature sensor 15.

[0056] The gas filling capacity 13 refers to a hermetically closed spaceformed between the first and second cutoff valves 12 and 17 when both ofthe first and second cutoff valves 12 and 17 are in a closed state.Concretely, for example, as shown in FIG. 4, in the case of constructingthe space between the first and second cutoff valves 12 and 17 by blockdevices such as the first cutoff valve 12, pressure sensor 14, andsecond cutoff valve 17 and channel blocks 21, 22, 23, and 24, anoutlet-side channel in a base block 12B of the first cutoff valve 12, achannel in the channel block 22, a channel in a base block 14B of thepressure sensor 14, a channel in the channel block 23, an inlet-sidechannel in a base block 17B of the second cutoff valve 17, and the likecorrespond to the gas filling capacity 13.

[0057] In FIG. 1 (and FIG. 7 to be described later), in order toemphasize the existence of the gas filling capacity 13, the gas fillingcapacity 13 is expressed a little different from the above-describeddefinition.

[0058] As shown in FIG. 1, the pulse shot type flow controller 1 isassembled in a semiconductor manufacturing apparatus. An upstream sideof the manual valve 11 is connected to a pressed process gas source. Adownstream side of the second cutoff valve 17 is connected to anevacuated vacuum vessel.

[0059] The pulse shot type flow controller 1 in FIG. 1 supplies, forexample, process gas of 0.1 to 100 L/min by repeating a pulse shot(opening/closing operation of the first cutoff valve 18 and, after that,opening/closing operation of the second cutoff valve 17) by thecontroller 19, that is, by a novel type called the pulse shot type.

[0060] In the pulse shot type flow controller 1 of FIG. 1, thecontroller 19 calculates the volume flow Q of process gas exhausted fromthe second cutoff valve 17 on the basis of an after-filling pressureP_(fill) and an after-exhaust pressure P_(redu) of the process gas inthe gas filling capacity 13 measured by the pressure sensor 14 and onthe basis of temperature T of the process gas in the gas fillingcapacity 13 measured by the temperature sensor 15.

[0061] Concretely, by performing a pulse shot (opening/closing operationof the first cutoff valve 12 and, after that, opening/closing operationof the second cutoff valve 17) once when the first and second cutoffvalves 12 and 17 are in a closed state, the pressure of the process gasin the gas filling capacity 13 between the first and second cutoffvalves 12 and 17 increases by the opening operation of the first cutoffvalve 12 and decreases by the opening operation of the second cutoffvalve 17.

[0062] Therefore, for example, as shown in FIG. 2, in the pulse shot ofthe first time, when a pressure after filling the process gas in the gasfilling capacity 13 is P1 _(fill), a pressure after exhausting theprocess gas of the gas filling capacity 13 is P1 _(redu), and volume ofthe process gas exhausted from the second cutoff valve 17 is Q1, thepulse shot type flow controller 1 of FIG. 1 calculates the volume Q1 ofthe process gas exhausted from the second cutoff valve 17 by the pulseshot of the first time by conversion in atmospheric pressure by thefollowing equation (1)′.

Q 1=V(P 1 _(fill) −P 1 _(redu))/1.0332*α  Equation (1)′

[0063] where “V” denotes the capacity of the gas filling capacity 13 and“α” indicates a correction factor (a correction term for a variationwhich is caused by flow characteristics of the first and second cutoffvalves 12 and 17).

[0064] Further, the pulse shot type flow controller 1 of FIG. 1 convertsthe volume Q1 of the process gas exhausted from the second cutoff valve17 by the pulse shot of the first time by 20° C. conversion inconsideration of the temperature T of the process gas in the gas fillingcapacity 13 in the equation (1)′ by the following equation (6)′.

Q 1(T=20)=Q 1×293/(T 1+273)   Equation (6)′

[0065] where “T1” denotes the temperature (° C.) of the process gas inthe gas filling capacity 13 in the pulse shot of the first time.“Q1(T=20)” is a value obtained by performing 20° C. conversion on thevolume Q1 of the process gas exhausted from the second cutoff valve 17by the pulse shot of the first time.

[0066] As shown in FIG. 2, in a pulse shot of the second time, when apressure after filling the process gas in the gas filling capacity 13 isP2 _(fill), a pressure after exhausting the process gas in the gasfilling capacity 13 is P2 _(redu), and the volume of the process gasexhausted from the second cutoff valve 17 is Q2, in a manner similar tothe equation (1)′, the pulse shot type flow controller 1 of FIG. 1calculates the volume Q2 of the process gas exhausted from the secondcutoff valve 17 by the pulse shot of the second time by conversion inatmospheric pressure by the following equation (1)″.

Q 2 =V(P 2 _(fill) −P 2 _(redu))/1.0332*α  Equation (1)″

[0067] Further, in the pulse shot type flow controller 1 of FIG. 1, alsoin the equation (1)″, the volume Q2 of the process gas exhausted fromthe second cutoff valve 17 by the pulse shot of the second time isobtained by 20° C. conversion in consideration of the temperature T ofthe process gas in the gas filling capacity 13 by the following equation(6)″.

Q 2(T=20)=Q 2×293/(T 2+273)   Equation (6)″

[0068] where “T2” denotes the temperature (° C.) of the process gas inthe gas filling capacity 13 in the pulse shot of the second time.“Q2(T=20)” is a value obtained by performing 20° C. conversion on thevolume Q2 of the process gas exhausted from the second cutoff valve 17by the pulse shot of the second time.

[0069] Since the pulse shot type flow controller 1 of FIG. 1 repeats thepulse shot (the opening/closing operation of the first cutoff valve 12and, after that, the opening/closing operation of the second cutoffvalve 17), for example, the volume flow Q(i, j) of the process gasexhausted from the second cutoff valve 17 by the i-th to j-th pulseshots is obtained by 20° C. conversion by the following equation (2)′.

Q(i,j)(T=20)=Qi(T=20)+ . . . +Qj−1(T=20)+Qj(T=20)   Equation (2)′

[0070] where “Q(i,j)(T=20)” is a value obtained by performing 20° C.conversion on the volume flow Q(i,j) of the process gas exhausted fromthe second cutoff valve 17 by the i-th to j-th pulse shots.

[0071] Therefore, the pulse shot type flow controller 1 of FIG. 1 canobtain the volume flow Q of the process gas exhausted from the secondcutoff valve 17, for example, per unit time by using the equation (2)′at any of the present and past time points by 20° C. conversion.

[0072] In the pulse shot type flow controller 1 of FIG. 1, as shown inFIG. 2, in the case where the pulse shot repeats in predetermined cyclesF (for example, 0.1 second), when an inverse number of the predeterminedcycle F is set as r (times/second), for example, a volume flow Q(i+1,i+r) of the process gas exhausted from the second cutoff valve 17 forone second from the (i+1)th pulse shot can be obtained by the followingequation by 20° C. conversion.

Q(i+1, i+r)(T=20)=Qi+1(T=20)+ . . . +Qi+r(T=20)   Equation (3)′

[0073] where “Q(i+1, i+r)(T=20)” is a value obtained by 20° C.conversion performed on the volume flow Q(i+1, i+r) of the process gasexhausted from the second cutoff valve 17 per second from the (i+1)thpulse shot in the case where the pulse shot is repeated in thepredetermined cycles F (that is, r (times/second)).

[0074] In FIG. 1, for example, in the case where the pressure conditionof a process gas source on the upstream side of the pulse shot type flowcontroller 1 and the pressure condition of a vacuum vessel on thedownstream side are stable, the values of volumes Qi+1(T=20), . . . ,and Qi+r(T=20) of the process gas exhausted from the second cutoff valve17 by the (i+1)th to the (i+r)th pulse shots are equal to each other.

[0075] In the pulse shot type flow controller 1 of FIG. 1, therefore, inthe case where the pressure condition of the process gas source on theupstream side of the pulse shot type flow controller 1 and the pressurecondition of the vacuum vessel on the downstream side of the pulse shottype flow controller 1 are stable, the following equation (4)′ obtainedby simplifying the equation (3)′ is used.

Q(i+1, i+r)(T=20)=r×Qi+1(T=20)   Equation (4)′

[0076] Therefore, in the pulse shot type flow controller 1 of FIG. 1, byusing the equation (4)′, the volume flow Q(i+1, i+r) of the process gasexhausted from the second cutoff valve 17 per second from the (i+1)thpulse shot can be obtained by 20° C. conversion using any one of thevolumes Qi+1(T=20), . . . , and Qi+r(T=20) of the process gas exhaustedfrom the second cutoff valve 17 by the (i+1)th to (i+r)th pulse shots.

[0077] Further, the pulse shot type flow controller 1 of FIG. 1 obtainsthe volume flow Q(S) of the process gas exhausted from the second cutoffvalve 17 of S seconds from the (i+1)th pulse shot by 20° C. conversionby the following equation (5)′ which is an application of the equation(4)′.

Q(S)(T=20)=S×Q(i+1, i+r)(T=20)   Equation (5)′

[0078] where “Q(S)(T=20)” denotes the value obtained by the volume flowQ(S) of the process gas exhausted from the second cutoff valve 17 for Sseconds from the (i+1)th pulse shot by 20° C. conversion in the casewhere the pulse shot is repeated in predetermined cycles F (that is,r(times/second)).

[0079] In the equation (5)′, (Qi+1, i+r)(T=20) in the equation (3)′ or(4)′ may be used.

[0080] Therefore, by using the equation (5)′, the pulse shot type flowcontroller 1 of FIG. 1 can obtain the volume flow Q(S) of the processgas exhausted from the second cutoff valve 17 for S seconds from the(i+1)th pulse shot by 20° C. conversion using the sum of volumes Qi+1, .. . , and Qi+r of the process gas exhausted from the second cutoff valve17 by the (i+1)th to (i+r)th pulse shots, or by 20° C. conversion usingany one of the volumes Qi+1, . . . , and Qi+r of the process gasexhausted from the second cutoff valve 17 by the (i+1)th to (i+r)thpulse shots.

[0081] The pulse shot type flow controller 1 of FIG. 1 controls thevolume flow of the process gas exhausted from the second cutoff valve 17by changing the mode of the pulse shot (opening/closing operation of thefirst cutoff valve 12 and, after that, opening/closing operation of thesecond cutoff valve 17) on the basis of the equations (1)′ to (5)′.

[0082] This point will be concretely described. For example, in the casewhere the pulse shot is repeated in predetermined cycles F as shown inFIG. 2, when the predetermined cycle F of repeating the pulse shot ischanged, the inverse number r (times/second) of the predetermined cycleF also changes. Consequently, the pulse shot type flow controller 1 ofFIG. 1 can control the volume flow Q(i+1, i+r)(T=20) of the process gasexhausted from the second cutoff valve 17 for one second from the(i+1)th pulse shot by the equations (3)′, (4)′, and (5)′.

[0083] Therefore, in the pulse shot type flow controller 1 of FIG. 1, bychanging the predetermined cycle F of repeating the pulse shot (theopening/closing operation of the first cutoff valve 12 and, after that,the opening/closing operation of the second cutoff valve 17), forexample, the volume flow Q(i+1, i+r)(T=20) of the process gas exhaustedfrom the second cutoff valve 17 for one second from the (i+1)th pulseshot can be controlled and, moreover, the volume flow Q of the processgas exhausted from the second cutoff valve 17 can be controlled.

[0084] According to the equation (1)′, the volume Q1 of the process gasexhausted from the second cutoff valve 17 by the pulse shot of the firsttime is influenced by the pressure P1 _(fill) after filling of theprocess gas in the gas filling capacity 13 and the pressure P1 _(redu)after exhaust of the process gas of the gas filling capacity 13.

[0085] In the pulse shot type flow controller 1 of FIG. 1, for example,in FIG. 2, by changing opening operation duration t1 of the secondcutoff valve 17, the after-exhaust pressure P1 _(redu) of the processgas in the gas filling capacity 13 can be changed. Consequently, bychanging the opening operation duration t1 of the second cutoff valve17, the volume Q1 of the process gas exhausted from the second cutoffvalve 17 by the pulse shot of the first time can be controlled.Similarly, by changing opening operation duration t2 of the secondcutoff valve 17, after-exhaust pressure P2 _(redu) of the process gas ofthe gas filling capacity 13 can be changed. Consequently, by changingthe opening operation duration t2 of the second cutoff valve 17, volumeQ2 of the process gas exhausted from the second cutoff valve 17 by thepulse shot of the second time can be controlled.

[0086] Therefore, in the pulse shot type flow controller 1 of FIG. 1, bychanging the opening operation durations t1, t2, . . . of the secondcutoff valve 17 for performing the pulse shot (the opening/closingoperation of the first cutoff valve 12 and, after that, theopening/closing operation of the second cutoff valve 17), for example,the volumes Q1, Q2, . . . of the process gas exhausted from the secondcutoff valve 17 by the pulse shots can be controlled and, moreover, thevolume flow Q of the process gas exhausted from the second cutoff valve17 can be controlled.

[0087] In the pulse shot type flow controller 1 of FIG. 1, in the casewhere the pulse shot is repeated in the predetermined cycle F and theinverse number of the predetermined cycle F is r (times/second) as shownin FIGS. 2 and 3, similarly, by changing opening operation durationsti+1, ti+2, ti+3, . . . , and ti+r of the second cutoff valve 17 of the(i+1)th to (i+r)th pulse shots, after-exhaust pressures Pi+1_(redu),Pi+2_(redu), Pi+3_(redu), . . . , and Pi+r_(redu) (not shown) of theprocess gas in the gas filling capacity 13 of the (i+1)th to (i+r)thpulse shots can be changed. Thus, volumes Qi+1(T=20), Qi+2(T=20),Qi+3(T=20), . . . , and Qi+r(T=20) of the process gas exhausted from thesecond cutoff valve 17 by the (i+1)th to (i+r)th pulse shots can becontrolled and, moreover, the volume flow Q of the process gas exhaustedfrom the second cutoff valve 17 can be controlled.

[0088] In the pulse shot type flow controller 1 of FIG. 1, when thepressure condition of the process gas source on the upstream side of thepulse shot type flow controller 1 and the pressure condition of thevacuum vessel on the downstream side of the pulse shot type flowcontroller 1 are stable, by changing all of the opening operationdurations ti+1, ti+2, ti+3, . . . , and ti+r of the second cutoff valve17 of the pulse shots starting from the (i+1)th pulse shot to the samevalue, the after-exhaust pressures Pi+1_(redu), Pi+2_(redu),Pi+3_(redu), . . . , and Pi+r_(redu) (not shown) of the process gas inthe gas filling capacity 13 by the pulse shots starting from the (i+1)thpulse shot change to the same value, and the volumes Qi+1(T=20),Qi+2(T=20), Qi+3(T=20), . . . , and Qi+r(T=20) of the process gasexhausted from the second cutoff valve 17 by the pulse shots startingfrom the (i+1)th pulse shot also change to the same value. Thus, thevolume flow Q of the process gas exhausted from the second cutoff valve17 can be controlled relatively easily.

[0089] An example of a pulse shot type flow controlling method executedby the pulse shot type flow controller 1 of FIG. 1 will now be describedwith reference to FIG. 5. The pulse shot type flow controlling methodshown in FIG. 5 is feedback control executed by the controller 19 in thepulse shot type flow controller 1. Specifically, first, in S10, thevolume flow Q of the process gas exhausted from the second cutoff valve17 per unit time is input as a “flow instruction value”. In S11, thepresent volume flow Q of the process gas exhausted from the secondcutoff valve 17 per unit time is obtained as a “calculated flow value”.In S12, a control deviation as the difference between the “flowinstruction value” and the “calculated flow value” is calculated.

[0090] In S13, to set the control deviation obtained in S12 to “0”, onthe basis of the equations (1)′ to (5)′ and equations (6)′ and (6)″,either a change in the predetermined cycle of the pulse shot(opening/closing operation of the first cutoff valve 12 and, after that,opening/closing operation of the second cutoff valve 17) or a change inthe opening operation duration of the second cutoff valve 17 by thepulse shot (opening/closing operation of the first cutoff valve 12 and,after that, opening/closing operation of the second cutoff valve 17) isdetermined. The result is transmitted to a control circuit built in thecontroller 19 in the pulse shot type flow controller 1. In the casewhere it is determined to change the predetermined cycle of a pulseshot, the routine advances to S14 where the predetermined cycle of thepulse shots is changed via a basic pulse output circuit built in thecontroller 19 of the pulse shot type flow controller 1. On the otherhand, in the case where it is determined to change the opening operationduration of the second cutoff valve 17 of each pulse shot, the routineadvances to step S15 where the opening operation duration of the secondcutoff valve 17 in each pulse shot is changed via a duty ratio varyingcircuit built in the controller 19 in the pulse shot type flowcontroller 1.

[0091] After that, in S16, n the basis of the after-filling pressureP_(fill) and the after-exhaust pressure P_(redu) of the process gas inthe gas filling capacity 13 measured by the pressure sensor 14 and onthe basis of the temperature T of the process gas in the gas fillingcapacity 13 measured by the temperature sensor 15, the volume flow Q ofthe process gas exhausted from the second cutoff valve 17 per unit timeis calculated by the equations (1)′ to (5)′, the equations (6)′ and (6)”or the like and the resultant value is used as the “calculated flowvalue” in S11.

[0092] In such a manner, the pulse shot type flow controller 1 canperform feedback control on the volume flow Q of the process gasexhausted from the second cutoff valve 17 per unit time. However,depending on the conditions, for example, as shown in FIG. 6, a deadzone may exist.

[0093] The “duty ratio” in FIG. 6 is a proportion (%) of the openingoperation duration to a time interval from the opening operation to theopening operation of the next time in the second cutoff valve 17.

[0094] As specifically described above, in the pulse shot type flowcontroller 1 and the pulse shot type flow controlling method executed bythe pulse shot type flow controller 1, by repeating the pulse shot (theopening/closing operation of the first cutoff valve 12 and, after that,the opening/closing operation of the second cutoff valve 17),calculating the volume flow Q of the process gas exhausted from thesecond cutoff valve 17 per unit time by the equations (1)′ to (5)′ onthe basis of the after-filling pressure P_(fill), after-exhaust pressureP_(redu), and the like of the process gas in the gas filling capacity 13measured by the pressure sensor 14 (S16) and, further, changing the modeof the pulse shot (the opening/closing operation of the first cutoffvalve 12 and, after that, the opening/closing operation of the secondcutoff valve 17) (S14 and S15), that is, by using a novel type calledthe pulse shot type, the volume flow Q of the process gas exhausted fromthe second cutoff valve 17 per unit time is controlled.

[0095] Therefore, in the pulse shot type flow controller 1 and the pulseshot type flow controlling method executed by the pulse shot type flowcontroller 1, as shown in FIG. 1, (1) there is no influence of aturbulent flow of the process gas and a device such as a laminar flowtube for forcefully suppressing turbulent flow of the process gasbecomes unnecessary. (2) It becomes unnecessary to interpose ameasurement device such as a tubule in a channel of the process gas. (3)The pressure of the process gas is not regulated, a device such as aregulator becomes unnecessary, and the components become simpler. Insuch a manner, the pulse shot type flow controller 1 and the pulse shottype flow controlling method can be released from the conventionalrestrictions.

[0096] In a semiconductor manufacturing apparatus, corrosive gas isused, gas replacement is performed, and a cutoff valve is often used forswitching a gas channel or the like. With respect to this point, thepulse shot type flow controller 1 and the pulse shot type flowcontrolling method executed by the pulse shot type flow controller 1 areused for a semiconductor manufacturing apparatus as shown in FIG. 1.Therefore, (4) since a measurement device such as a tubule is not used,abnormality such as clogging caused by corrosion does not occur. (5)Since there is no dead volume, gas replacement can be executed withreliability. (6) By using the first and second cutoff valves 12 and 17for switching a gas channel, the number of cutoff valves used forswitching a gas channel or the like can be reduced.

[0097] It was found out through experiments conducted by the applicantof the present invention that when pulse shots are performed at highfrequency such that the filling/exhausting cycle is less than onesecond, the pressure waveform of the process gas in the gas fillingcapacity 13 as shown in FIG. 8 is obtained. Specifically, when suchhigh-frequency pulse shots are made, a temperature rise of the processgas in the gas filling capacity 13 occurs due to adiabatic compressionat the time of filling, and a temperature drop of the process gas in thegas filling capacity 13 occurs due to adiabatic expansion at the time ofexhaust. Consequently, the pressure waveform of the process gas in thegas filling capacity 13 becomes as shown in FIG. 8.

[0098] To be specific, after a temperature change occurs at each of thefilling time and the exhaust time, heat exchange occurs in the gasfilling capacity 13. When the filling/exhaust cycle becomes shorter, theheat exchange continues also in a sealed state after thefilling/exhaust, and both temperature and pressure continue changing.Therefore, it is useless to measure the pressure during the period. Itis necessary to measure the pressure after completion of the heatexchange or after the temperature decreases to a temperature at whichthere is no problem with precision, and use the measured temperature forthe flow calculation.

[0099] In the case of making pulse shots at high frequency, however,high-precision flow measurement cannot be performed. In order to solvethe problem, there is a method of measuring pressure at predeterminedtimings in consideration of a temperature change amount, multiplying thepressure with a correction factor, and using the result value. However,the temperature change caused by adiabatic compression and adiabaticexpansion is determined by a ratio of specific heat peculiar to the kindof gas and a ratio between pressures before and after filling/exhaust,so that it is not constant. A correction factor has to be calculated inadvance by a flow test under necessary conditions. Consequently, themethod is not practical.

[0100] Also in the pulse shot type according to the invention, when theflow changes, average temperature of the process gas in the gas fillingcapacity 13 changes. To be specific, when a constant flow occurs, theprocess gas of which temperature decreased due to adiabatic expansion atthe time of exhaust is heated by the gas filling capacity 13 at the timeof sealing, and the adiabatic compression caused by filling occurs againin the gas filling capacity 13, so that a temperature rise higher thanthat before the adiabatic expansion occurs. The temperature changesuntil an equilibrium state is obtained among the increased temperature,external air, and peripheral devices. Since the degree of a temperaturedrop caused by the adiabatic expansion differs according to the flow, anequilibrium state temperature also changes.

[0101] Consequently, it is necessary to allow precision deterioration bythe amount of the temperature rise or wait for a drop of the increasedtemperature to a temperature at which no influence is exerted. In thismanner, however, pulse shots can be made at low frequency, and themethod is not practical.

[0102] There is also a method of using a measurement value of thetemperature sensor 15. From the viewpoint of an equation of state ofgas, if instantaneous pressure and temperature at an arbitrary timepoint can be measured in a sealed state after filling/exhaust in the gasfilling capacity 13, an equation of state can be derived. The number ofmoles of the process gas in the gas filling capacity 13 at that timepoint can be specified and the volume flow Q of the process gasexhausted from the second cutoff valve 17 can be calculated.

[0103] The equation of state of the process gas in the gas fillingcapacity after filling is expressed as follows.

P _(fill) *V=n _(fill) *R*T _(fill)

[0104] Consequently, the number of moles of the process gas in the gasfilling capacity after filling is expressed as follows.

n _(fill)=(P _(fill) *V)/(R*T _(fill))

[0105] “n_(fill)” denotes the number of moles of the process gas in thegas filling capacity at the time of filling, “R” denotes a gas constant,and “T_(fill)” indicates the temperature of the process gas in the gasfilling capacity after filling.

[0106] On the other hand, the equation of state of the process gas inthe gas filling capacity after exhaust is expressed as follows.

P _(redu) *V=n _(redu) *R*T _(redu)

[0107] Consequently, the number of moles of the process gas in the gasfilling capacity after exhaust is as follows.

n _(redu)=(P _(redu) *V)/(R*T _(redu))

[0108] “n_(redu)” denotes the number of moles of the process gas in thegas filling capacity after exhaust, and “T_(redu)” denotes thetemperature of the process gas in the gas filling capacity exhaust.

[0109] The number n_(ex) of moles of the process gas exhausted from thesecond cutoff valve 17 is expressed as follows. $\begin{matrix}{n_{ex} = {n_{fill} - n_{redu}}} \\{= {{( {P_{fill}*V} )/( {R*T_{fill}} )} - {( {P_{redu}*V} )/( {R*T_{redu}} )}}} \\{= {V/{R( {{P_{fill}/T_{fill}} - {P_{redu}/T_{redu}}} )}}}\end{matrix}$

[0110] Therefore, the volume V_(ex) of the process gas exhausted fromthe second cutoff valve 17 is expressed as follows. $\begin{matrix}{V_{ex} = {n_{ex}*R*{273.15/101.3}}} \\{= {2.6962*R*n_{ex}}} \\{= {2.6962*V*( {{P_{fill}/T_{fill}} - {P_{redu}/T_{redu}}} )}}\end{matrix}$

[0111] Consequently, the volume flow Q of the process gas exhausted fromthe second cutoff valve 17 is derived as follows. $\begin{matrix}\begin{matrix}{Q = {V_{ex}*r*60}} \\{= {161.17*r*V*( {{P_{fill}/T_{fill}} - {P_{redu}/T_{redu}}} )}}\end{matrix} & {{Equation}\quad (7)}\end{matrix}$

[0112] Therefore, if the instantaneous pressure and temperature at anarbitrary time point can be measured in a sealed state afterfilling/exhaust in the gas filling capacity 13, the volume flow Q of theprocess gas exhausted from the second cutoff valve 17 can be calculatedby the equation (7).

[0113] However, it is extremely difficult to perform high-speedmeasurement of the temperature of gas having low density because atemperature sensor for measuring the temperature of corrosive gas isgenerally covered with corrosive-resistant metal, resin, ceramic or thelike, so that the quantity of heat is large and high response cannot beobtained. By a very thin thermocouple and a temperature sensor made ofsemiconductor silicon, high response can be obtained but the temperatureof corrosive gas cannot be measured. In the current state, a corrosiontemperature sensor capable of measuring a temperature changeaccompanying high-speed adiabatic compression/expansion in a real timemanner does not exist. That is, in the current state, it is impossibleto measure a temperature change in the process gas in the gas fillingcapacity 13 in a real time manner by the temperature sensor 15.

[0114] On the other hand, the pressure can be measured with response of1 second or less. Therefore, the pulse shot type flow controller 1according to the embodiment and the pulse shot type flow controllingmethod executed by the pulse shot type controller 1 realizeshigh-precision flow measurement by measuring a pressure changeproportional to a temperature change.

[0115] First, in a sealed state after filling, pressure in the heatequilibrium state is estimated from a pressure value and a pressurechange rate. For example, a tangent of a pressure change curve iscalculated from pressure values measured at predetermined timeintervals, and pressure after a time constant which is calculated inadvance is computed and used as pressure in the heat equilibrium stateafter filling.

[0116] Similarly, in the sealed state after exhaust, pressure in theheat equilibrium state is estimated from the pressure value and thepressure change rate. For example, a tangent of a pressure change curveis obtained from pressure values measured at predetermined timeintervals, and pressure after a time constant which is calculated inadvance is computed and used as pressure in the heat equilibrium stateafter exhaust.

[0117] Since a pressure change at the time of sealing is not always be asimple primary response, the pressure in the heat equilibrium state isused and computed while switching a proper time constant in accordancewith the gas kind, primary pressure, pressure drop amount due to theexhaust, and the like.

[0118] The pressures of filling and exhaust computed as described above(after-filling estimated pressure and after-exhaust estimated pressure)are set as the after-filling pressure P_(fill) and the after-exhaustpressure P_(redu), the average temperature obtained from the temperaturesensor 15 is used as an equilibrium temperature, and the volume flow Qof the process gas exhausted from the second cutoff valve 17 iscalculated by the equation (7).

[0119] A method of calculating the volume flow Q of the process gasexhausted from the second cutoff valve 17 executed by the controller 19in the pulse shot type flow controller 1 on the basis of theabove-described concept will now be described. First, a method ofcalculating a time constant will be described with reference to FIGS. 9and 10. Since the pressure change is deviated from a primary response,the pressure change cannot be the as a time constant in accuratemeaning. However, it will be called a “time constant” for conveniencesince it is conceptually close to a time constant.

[0120] First, the case of obtaining a time constant at the time offilling the process gas to the gas filling capacity 13 will now bedescribed with reference to FIG. 9. First, a time point of closing ofthe first cutoff valve 12 is set as t0 (reference point of time). Afterlapse of the time t1 in which a pressure change in after closing thefirst cutoff valve can be reliably detected with an allowance ofresponse delay time (about 1 msec) of the first cutoff valve 12 (forexample, after lapse of 3 msec, t1=3 msec), pressure measurement of thefirst time is conducted by the pressure sensor 14. The measurement valueat this time is displayed as (t1, p1). Further, after lapse ofpredetermined time (for example, after lapse of 1 msec, t2=4 msec),pressure measurement of the second time is executed by the pressuresensor 14. The measurement value at this time is indicated as (t2, p2).Further, after lapse of predetermined time (for example, after lapse of1 msec, t3=5 msec), pressure measurement of the third time is performedby the pressure sensor 14. The measurement value at this time isexpressed as (t3, p3).

[0121] The time interval of pressure measurement does not have to be thesame but has to be a fixed time. In order to suppress influence of noiseor the like, pressures at measurement points are measured a plurality oftimes (for example, eight times every 10 μsec) and an average value ofthe measured pressures may be used.

[0122] Further, after lapse of sufficient time (for example, after lapseof 1 sec, t4=1005 msec), pressure measurement of the fourth time isperformed by the pressure sensor 14. The measurement value at this timeis expressed as (t4, p4).

[0123] A time constant ΔTs of a pressure change at the time of fillingis calculated from the measurement results. As an example, a timeconstant at the time point t2 is obtained. First, an equation of atangential line L passing (t2, p2) from (t1, p1), (t2, p2), (t3, p3),and (t4, p4) is obtained by the following equation.

Tangential line L:P=(p 3 −p 1)/(t 3 −t 1)*(t−t 2)+p 2   Equation (8)

[0124] Although it is obtained by the simple method, the equation of thetangential line L may be also obtained by using other methods such asthe least square method.

[0125] Subsequently, time at which the tangential line L matches p4 isobtained, and t2 is subtracted from the time. The result of thecalculation is the time constant ΔTs at the time point t2. The timeconstant ΔTs is expressed by the following equation.

ΔTs=(p 4 −p 2)*(t 3 −t 1)/(p 3 −p 1)−t 2

[0126] ΔP(=p4−p2) shown in FIG. 9 denotes a pressure drop amount from p2to the pressure p4 at the equilibrium temperature and reflects thetemperature drop amount.

[0127] The case of obtaining a time constant at the time of exhaustingthe process gas in the gas filling capacity 13 will now be describedwith reference to FIG. 10. First, a time point of closing of the secondcutoff valve 17 is set as t0′ (reference point of time). After lapse ofthe time t1′ in which a pressure change after closing the second cutoffvalve 17 can be reliably detected with an allowance of response delaytime (about 1 msec) of the second cutoff valve 17 (for example, afterlapse of 3 msec, t1′=3 msec), pressure measurement of the first time isconducted by the pressure sensor 14. The measurement value at this timeis displayed as (t1′, p1′). Further, after lapse of predetermined time(for example, after lapse of 1 msec, t2′=4 msec), pressure measurementof the second time is executed by the pressure sensor 14. Themeasurement value at this time is indicated as (t2′, p2′). After lapseof predetermined time (for example, after lapse of 1 msec, t3′=5 msec),pressure measurement of the third time is performed by the pressuresensor 14. The measurement value at this time is expressed as (t3′,p3′).

[0128] The time interval of pressure measurement does not have to be thesame time but has to be fixed time. In order to suppress influence ofnoise or the like, pressures at measurement points are measured aplurality of times (for example, eight times every 10 μsec) and anaverage value of the measured pressures may be used.

[0129] Further, after lapse of sufficient time (for example, after lapseof 1 sec, t4′=1005 msec), pressure measurement of the fourth time isperformed by the pressure sensor 14. The measurement value at this timeis expressed as (t4′, p4′).

[0130] A time constant ΔTe of a pressure change at the time of exhaustis calculated from the measurement results. As an example, a timeconstant at the time point t2′ is obtained. First, an equation of atangential line L′ passing (t2′, p2′) from (t1′, p1′), (t2′, p2′), (t3′,p3′), and (t4′, p4′) is obtained by the following equation.

Tangential line L′:P=(p 3′−p 1′)/(t 3′−t 1′)*(t−t2 ′)+p2′  Equation (9)

[0131] Although it is obtained by the simple method, the equation of thetangential line L′ may be also obtained by using other methods such asthe least square method.

[0132] Subsequently, time at which the tangential line L′ coincides withp4′ is obtained, and t2′ is subtracted from the obtained time. Theresult of the calculation is the time constant ΔTs at the time pointt2′. The time constant ΔTs is expressed by the following equation.

ΔTs=(p 4′−p 2′)*(t 3′−t 1′)/(p 3′−p 1′)−t 2′

[0133] ΔP′(=p4′−p2′) shown in FIG. 10 denotes a pressure drop amountfrom p2′ to the pressure p4′ at the equilibrium temperature and reflectsthe temperature drop amount.

[0134] By using the time constants ΔP and ΔP′ calculated as describedabove, the volume flow Q of the process gas exhausted from the secondcutoff valve 17 is calculated. The calculation method will be describedwith reference to FIG. 10. The volume flow Q of the process gas is alsocalculated by the controller 19.

[0135] The volume flow Q of the process gas is calculated by executingthe following arithmetic operation every cycle of the pulse shot. First,the first cutoff valve 12 is opened to fill the gas filling capacity 13with the process gas for specified time. After lapse of the specifiedtime t1 since the time point at which the first cutoff valve 12 wasclosed, the pressure p1 is measured by the pressure sensor 14.Similarly, after lapse of specified time since the time point at whichthe first cutoff valve 12 was closed, pressure p2 is measured by thepressure sensor 14. After lapse of specified time t3 since the timepoint at which the first cutoff valve 12 was closed, pressure p3 ismeasured by the pressure sensor 14. From a combination of the times andpressures at the three points, an equation of the tangential line Lpassing (t2, p2) is obtained by the equation (8).

[0136] The pressure Ps after the known time constant ΔTs is computed bythe following equation and set as stable pressure Ps after filling(after-filling estimated pressure).

Ps=(p 3−p 1)/(t 3−t 1)*ΔTs+p 2

[0137] After lapse of adjusted predetermined time, the second cutoffvalve 17 is opened to exhaust the process gas and then is closed. Afterlapse of specified time t1′ from the time point at which the secondcutoff valve 17 was closed, pressure p1′ is measured by the pressuresensor 14. Similarly, after lapse of specified time t2′ since the timepoint at which the second cutoff valve 17 was closed, pressure p2′ ismeasured by the pressure sensor 14. After lapse of specified time t3′since the time point at which the second cutoff valve 17 was closed,pressure p3′ is measured by the pressure sensor 14. From a combinationof the times and pressures at the three points, an equation of thetangential line L′ passing (t2′, p2′) is obtained by the equation (9).

[0138] The pressure Pe after the known time constant ΔTe is obtained bythe following equation and set as stable pressure Pe after exhaust(after-exhaust estimated pressure).

Pe=(p 3′−p 1′)/(t 3′−t 1′)*ΔTe+p 2′

[0139] The volume flow ΔQ of exhaust from the second cutoff valve 17 bythe pulse shot of one cycle is computed by the following equation usingPs and Pe which are calculated as described above.

ΔQ=V(Ps−Pe)/T

[0140] “T” denotes average temperature (absolute temperature) in the gasfilling capacity 13.

[0141] Although the pressures Ps and Pe in a stable state have beenestimated in this case, it is also possible to estimate temperatures T2and T2′ at time points t2 and t2′ and calculate the volume flow ΔQ ofexhaust from the second cutoff valve 17 by the pulse shot of one cyclefrom the following equation.

[0142] Since T2=T*p2/Ps and T2′=T*p2′/Pe, the volume flow ΔQ can beobtained as follows.

ΔQ=V(p 2/T 2−p 2′/T 2′)

[0143] On the basis of the volume flow ΔQ calculated as described above,flow control is executed by the controller 19. Concretely, on the basisof the deviation of ΔQ from the volume flow ΔQo of exhaust from thesecond cutoff valve 17 by the pulse shot of one cycle computed from aflow instruction value, the width of a pulse applied to the secondcutoff valve 17 in the pulse shot of the next cycle is properlyincreased/decreased. Specifically, when ΔQ is smaller than ΔQo, thepulse width is increased. When ΔQ is larger than ΔQo, the pulse width isdecreased. As a method of increasing/decreasing the pulse width,proportional control for giving increase/decrease in proportion to thedeviation, integration control of adding the deviation at a constantrate, differential control for making a large correction to a sharpchange in the deviation, and the like may be properly combined.

[0144] FIGS. 13 to 15 show results of calculation of the volume flow Qcalculated by the controller 19 when two kinds of gases (N₂ and Ar) arepassed at a specified flow rate (800 sccm) to the pulse shot type flowcontroller 1. FIG. 13 shows various data at the time of filling. FIG. 14shows various data at the time of exhaust. FIG. 15 shows a calculationresult. FIG. 12 shows the pressure waveform at the time of calculation.

[0145] As shown in FIG. 12, the rate of a pressure change differsaccording to the gas kind for the reason that the ratio of specific heatvaries according to the gas kind. With respect to the N₂ gas and the Argas used this time, it is understood that the temperature change of theAr gas having a higher ratio of specific heat is larger, so that thepressure change of the Ar gas is also larger.

[0146] First, various data at the time of calculating the volume flow Qof the N₂ gas is examined. At the time of filling the N₂ gas, as shownin FIG. 13, the gas filling capacity 13 was filled with the N₂ gas andthe pressure p1 at time t0 when the first cutoff valve 12 was closed was350.39 kPa. The pressure p1 at time t1 after lapse of 3 msec since t0was 350.22 kPa. Further, the pressure p2 at time t2 after lapse of 1msec was 350.13 kPa. Further, the pressure p3 at time t3 after lapse of1 msec was 349.97 kPa. As described above, it is understood that thepressure of the N₂ gas in the gas filling capacity 13 graduallydecreases after the second cutoff valve 17 is closed. On the basis ofthe measured pressure, the time constant ΔTs at the time point t2 wascalculated as 16 msec. The pressure Ps after the time constant ΔTs wascalculated as 348.1 kPa.

[0147] On the other hand, at the time of exhaust of the N₂ gas, as shownin FIG. 14, the pressure p1′ at time t0′ at which the second cutoffvalve 17 was closed after the second cutoff valve 17 was opened toexhaust the N₂ gas from the gas filling capacity 13 was 288.08 kPa. Thepressure p1′ at time t1′ after lapse of 4 msec since t0′ was 287.17 kPa.Further, the pressure p2′ at time t2′ after lapse of 1 msec was 287.39kPa. Further, the pressure p3′ at time t3′ after lapse of 1 msec was287.55 kPa. As described above, it is understood that the pressure ofthe N₂ gas in the gas filling capacity 13 gradually increases after thesecond cutoff valve 17 is closed. On the basis of the measured pressure,the time constant ΔTe at the time point t2′ was calculated as 50 msec.The pressure Pe after the time constant ΔTe was calculated as 296.8 kPa.

[0148] Since the average temperature T of the N₂ gas is 300K, the volumeV of the gas filling capacity 13 is 1.75 cc, and the pulse frequency ris 16.67 Hz, as shown in FIG. 15, the volume flow Q of exhaust from thesecond cutoff valve 17 was calculated as 807.4 sccm. An error of thecalculation result is 0.92% which is very small. That is, it can be thethat the volume flow Q of exhaust from the second cutoff valve 17 iscalculated with high precision.

[0149] Next, various data used at the time of calculating the volumeflow Q of the Ar gas will be examined. As shown in FIG. 13, the pressurep1 at time t0 at which the gas filling capacity 13 was filled with theAr gas and the first cutoff valve 12 was closed was 350.00 kPa. Thepressure p1 at time t1 after lapse of 3 msec since t0 was 349.56 kPa.Further, the pressure p2 at time t2 after lapse of 1 msec was 349.41kPa. Further, the pressure p3 at time t3 after lapse of 1 msec was349.12 kPa. As described above, it is understood that the pressure ofthe Ar gas in the gas filling capacity 13 gradually decreases after thesecond cutoff valve 17 was closed. On the basis of the measuredpressure, the time constant ΔTs at the time point t2 was calculated as13 msec. The pressure Ps after the time constant ΔTs was calculated as346.6 kPa.

[0150] On the other hand, at the time of exhaust of the Ar gas, as shownin FIG. 14, the pressure p1′ at time t0′ at which the second cutoffvalve 17 was closed after the second cutoff valve 17 was opened toexhaust the Ar gas from the gas filling capacity 13 was 281.98 kPa. Thepressure p1′ at time t1′ after lapse of 4 msec since t0′ was 282.01 kPa.Further, the pressure p2′ at time t2′ after lapse of 1 msec was 282.32kPa. Further, the pressure p3′ at time t3′ after lapse of 1 msec was282.66 kPa. As described above, it is understood that the pressure ofthe Ar gas in the gas filling capacity 13 gradually increases after thesecond cutoff valve 17 is closed. On the basis of the measured pressure,the time constant ΔTe at the time point t2′ was calculated as 42 msec.The pressure Pe after the time constant ΔTe was calculated as 296.1 kPa.

[0151] Since the average temperature T of the Ar gas is 300K, the volumeV of the gas filling capacity 13 is 1.75 cc, and the pulse frequency ris 16.67 Hz, as shown in FIG. 15, the volume flow Q of exhaust from thesecond cutoff valve 17 was calculated as 794.0 sccm. An error of thecalculation result is as small as 0.75%. That is, it can be the that thevolume flow Q of exhaust from the second cutoff valve 17 is calculatedwith high precision.

[0152] The volume flow Q of exhaust from the second cutoff valve 17 ofeven gases with different ratios of specific heat can be calculated withhigh precision.

[0153]FIG. 16 shows a result of calculating the volume flow Q of exhaustfrom the second cutoff valve 17 without considering a temperature changeaccompanying adiabatic compression/expansion, that is, a result ofcalculation of the volume flow Q by using the equations (1)′ to (5)′. Inthis case, with respect to the N₂ gas, the after-filling pressureP_(fill) was measured as 349.52 kPa, and the after-exhaust pressureP_(redu) was measured as 288.52 kPa, so that the pressure difference is61.00 kPa, and the volume flow Q of exhaust from the second cutoff valve17 was calculated as 959 sccm. An error of the calculation result is12%.

[0154] With respect to the Ar gas, the after-filling pressure P_(fill)was measured as 348.34 kPa and the after-exhaust pressure P_(redu) wasmeasured as 284.23 kPa, so that the pressure difference was 64.11 kPa,and the volume flow Q of exhaust from the second cutoff valve 17 wascalculated as 1008 sccm. An error of the calculation result is 12.6%.

[0155] As described above, in the case of making pulse shots at highfrequency, without considering a temperature change accompanyingadiabatic compression/expansion, the volume flow Q of exhaust from thesecond cutoff valve 17 cannot be calculated with high precision. Acalculation error becomes large for a gas having a high ratio ofspecific heat.

[0156] As described in detail, in the case of making pulse shots at highfrequency in the pulse shot type flow controller 1, by considering atemperature change accompanying adiabatic compression/expansion, anerror of the volume flow Q of exhaust from the second cutoff valve 17can be reduced by 10% or more. That is, even in the case of making pulseshots at high frequency, the flow control can be performed with veryhigh precision by suppressing influences of a temperature changeaccompanying adiabatic compression/expansion.

[0157] By realizing pulse shots of high frequency, the following effectsare obtained. A change interval of pulses can be further shortened, anda pressure change and a flow change according to the pulse can befurther reduced. The same flow rate as that in the case of pulse shotsof low frequency can be assured with a smaller gas filling capacity.Further, in the case of the same gas filling capacity, a higher flow canbe assured. A flow control of higher precision can be performed onvarious gases of different degrees of a temperature change (the ratio ofspecific heat) caused by an adiabatic change.

[0158] The present invention is not limited to the foregoing embodimentbut can be variously changed without departing from the gist.

[0159] For example, in the pulse shot type flow controller 1 and thepulse shot type flow controlling method executed by the pulse shot typeflow controller 1, at the time of calculating the volume flow Q ofprocess gas exhausted from the second cutoff valve 17 per unit time(S16), 20° C. conversion is performed by the equations (6)′, (6)″, orthe like on the basis of the temperature T of the process gas in the gasfilling capacity 13 measured by the temperature sensor 15. Iftemperature expansion of the process gas can be ignored, 20° C.conversion may be omitted.

[0160] In the pulse shot type flow controller 1 and the pulse shot typeflow controlling method executed by the pulse shot type flow controller1, the opening operation duration of the second cutoff valve 17 in eachpulse shot is changed via a duty ratio varying circuit built in thecontroller 19 of the pulse shot type flow controller 1 in S15. Also inthe case where the opening operation duration of the first cutoff valve12 by each pulse shot is changed, the after-filling pressure P_(fill)and the after-exhaust pressure P_(redu) of the process gas of the gasfilling capacity 13 of each pulse shot change, so that the volume flow Qof the process gas exhausted from the second cutoff valve 17 per unittime can be controlled.

[0161] Alternately, the opening operation time of the first cutoff valve12 may be changed not for controlling the volume flow of the process gasbut for regulation of pressure supplied to the gas filling capacity 13.In the pulse shot type flow controller 1 and the pulse shot type flowcontrolling method executed by the pulse shot type flow controller 1,when the first cutoff valve 12 is opened to fill the gas fillingcapacity 13 with the process gas, a filling pressure state of the gasfilling capacity 13 can be monitored by the pressure sensor 14.Consequently, at the time point when the pressure reaches predeterminedregulated pressure, the first cutoff valve 12 can be closed. Therefore,even if a gas of which pressure exceeds a withstand pressure of thepressure sensor 14 is supplied from a process gas source, the firstcutoff valve 12 can be closed so that the pressure cannot exceed thewithstand pressure of the pressure sensor 14. In practice, the firstcutoff valve 12 is closed with an allowance of a certain degree on thebasis of a pressure increase curve and the response at the time ofclosing of the first cutoff valve 12. Since the action is the same asthe action of the regulator 11 for regulating pressure, the regulator 11can be made unnecessary.

[0162] Therefore, the upper limit of the pressure on the primary side(upstream side of the gas filling capacity 13) is substantiallydetermined by the withstanding pressure of the first cutoff valve 12,and a pressure sensor of which withstand pressure is low can be used.The pressure sensor of low withstand pressure has relatively higherresolution as compared with a pressure sensor of high withstandpressure, so that the flow can be measured with high precision. Sincethe regulator 11 becomes unnecessary, in the case where supply pressureof the process gas is low, there is no pressure loss which occurs in theregulator 11, and the flow can be measured with higher precision.

[0163] In the pulse shot type flow controller 1 and the pulse shot typeflow controlling method executed by the pulse shot type flow controller1, in S13, either changing of a predetermined cycle of each pulse shot(opening/closing operation of the first cutoff valve 12 and, after that,opening/closing operation of the second cutoff valve 17) or changing ofopening operation duration of the second cutoff valve 17 in each pulseshot (opening/closing operation of the first cutoff valve 12 and, afterthat, opening/closing operation of the second cutoff valve 17) isdetermined. Alternately, by making a decision to simultaneously performboth of the changes, the control deviation obtained in S12 can be set to“0”.

[0164] In the pulse shot type flow controller 1 and the pulse shot typeflow controlling method executed by the pulse shot type flow controller1, as shown in FIG. 7, by providing a nozzle 16 on the upstream side ofthe second cutoff valve 17, (the pressure waveform of) the process gasin the gas filling capacity 13 in each pulse shot can be furtherstabilized. By providing a filter 18 on the downstream side of thesecond cutoff valve 17, (the pressure waveform) of the process gasexhausted from the second cutoff valve 17 can be further stabilized.

[0165] It is also possible to automatically calculate the time constantsΔTs and ΔTe which become necessary in the case of making pulse shots athigh frequency by performing a learning operation described below.First, an unknown necessary gas is supplied, the first cutoff valve 12is opened, and the second cutoff valve 17 is closed to obtain a fillingstate. Next, both the first and second cutoff valves 12 and 17 areclosed to obtain a sealed state of the gas filling capacity 13 and thestate is left sufficiently until a heat equilibrium state is obtained.The second cutoff valve 17 is opened only by short time to cause apressure drop corresponding to a control flow, after that, the secondcutoff valve 17 is closed again, a pressure value and a pressure changerate are measured, and a tangential line of a pressure change curve isderived. The state is sufficiently left until a temperature equilibriumstate is obtained and the pressure in the equilibrium state (asymptote)is measured again. From the tangential line and the asymptote, a timeconstant at the time of control flow is obtained. As necessary, it isalso possible to repeat the processes a plurality of times, calculate anaverage value, and use the average value as a time constant. After that,the control flow is generally measured at some points at the time ofboth filling and exhaust. On the basis of the data obtained by themeasurement, a time constant in a necessary control flow isautomatically calculated by complementation.

[0166] In such a manner, a necessary time constant of an arbitraryunknown gas can be obtained even if physical properties of the gas areunknown, so that high-precision flow control can be performed.

[0167] When gas kinds are different from each other because of thephysical properties (viscosity, ratio of specific heat, and the like),flowabilities differ from each other by ten times or more with respectto the same cutoff valve (orifice). When the first and second cutoffvalves 12 and 17 are designed for a gas having low flowability, theprecision of flow control for a gas having high flowability deterioratesto {fraction (1/10)}. For example, when the second cutoff valve 17(orifice) is designed so as to make a gas having low flowability (C₃F₄)flow at 1 SLM with opening time 25 msec of the second cutoff valve 17(including waste time of 5 msec and a proportional band is 20 msec), agas having high flowability (He) flows at the flow rate of 1 SLM withopening time of 7 msec of the second cutoff valve 17. There is onlyabout 2 msec as a proportional band, control resolution deteriorates byten times and, particularly, controllability at the time of low flowrate deteriorates. The valve open time of 23 msec which is not used as aresult is wasted.

[0168] On the other hand, when proper opening time of the second cutoffvalve 17 is set in accordance with viscosity, the ratio of specificheat, and the like peculiar to a gas, it is necessary to change thesetting of the opening time of the second cutoff valve 17 for each gaskind used, and it is inconvenient.

[0169] As the second cutoff valve 17, a proportional valve at which anopening (flow characteristic) proportional to a current value isobtained may be used. To be specific, the second cutoff valve 17 is notsimply opened/closed but can be opened/closed at an arbitrary opening(flow characteristic of an orifice). It is sufficient to obtain andrecord a proper opening (current) by switching the opening (current) ofthe second cutoff valve 17 so that opening time of the second cutoffvalve 17 necessary to cause a pressure drop corresponding to a necessarymaximum flow becomes almost the maximum value (maximum value including acontrol allowance and safety) of the opening time of the second cutoffvalve 17. For example, in the case where control time of 30 msec isallocated for the second cutoff valve 17, the opening (current) of thesecond cutoff valve 17 is obtained so that a pressure drop correspondingto the maximum flow occurs with the opening time of 25 msec of thesecond cutoff valve 17.

[0170] In such a manner, proper opening is set for the second cutoffvalve 17 by learning to supply an arbitrary gas, so that proper openingtime of the second cutoff valve 17 according to the flow is assured. Atthe maximum flow, most of the allocated control time is opening time.Also at a small flow, opening time in which necessary resolution can beassured is set. Therefore, for different gas kinds or an unknown gaskind, proper opening time of the second cutoff valve 17 can be assured,and controllability does not deteriorate. Thus, for any gas kind, theflow control can be performed with high precision.

[0171] Industrial Applicability

[0172] As described above, in the pulse shot type flow controller andthe pulse shot type flow controlling method of the invention, a noveltype of a pulse shot type is used. That is, a pulse shot of performingthe opening/closing operation of the first cutoff valve and, after that,performing the opening/closing operation of the second cutoff valve isrepeated, a volume flow of a gas exhausted from the second cutoff valveis calculated on the basis of an after-filling pressure and anafter-exhaust pressure of gas filling capacity measured by the pressuresensor, and the mode of the pulse shot is changed, thereby controllingthe volume flow of the gas exhausted from the second cutoff valve. (1)There is no influence of a turbulent flow of the process gas and adevice such as a laminar flow tube for forcefully suppressing turbulentflow of the gas becomes unnecessary. (2) It becomes unnecessary tointerpose a measurement device such as a tubule in a channel of the gas.(3) The pressure of the gas is not regulated, a device such as aregulator becomes unnecessary, and the components become simpler. Insuch a manner, the pulse shot type flow controller and the pulse shottype flow controlling method can be released from the conventionalrestrictions.

[0173] In a semiconductor manufacturing apparatus, corrosive gas isused, gas replacement is performed, and a cutoff valve is often used forswitching a gas channel or the like. Consequently, by using the pulseshot type flow controller and the pulse shot type flow controllingmethod of the invention for a semiconductor manufacturing apparatus, (4)since a measurement device such as a tubule is not used, abnormalitysuch as clogging caused by corrosion does not occur. (5) Since there isno dead volume, gas replacement can be executed with reliability. (6) Byusing the first and second cutoff valves for switching a gas channel,the number of cutoff valves used for switching a gas channel or the likecan be reduced.

[0174] In the case of making pulse shots at high frequency, byconsidering a temperature change accompanying adiabaticcompression/expansion, a flow control can be performed with very highprecision.

[0175] By realizing pulse shots of high frequency, the following effectsare obtained. A change interval of pulses can be further shortened, anda pressure change and a flow change according to the pulse can befurther reduced. The same flow rate as that in the case of pulse shotsof low frequency can be assured with a smaller gas filling capacity.Further, in the case of the same gas filling capacity, a higher flow canbe assured. A flow control of higher precision can be performed onvarious gases of different degrees of a temperature change (the ratio ofspecific heat) caused by an adiabatic change.

1. A pulse shot type flow controller comprising: a first cutoff valveconnected to a gas source; a second cutoff valve connected to the firstcutoff valve; a gas filling capacity between the first and second cutoffvalves; and a pressure sensor for measuring pressure in the gas fillingcapacity, wherein a pulse shot of performing opening/closing operationof the first cutoff valve and, after that, performing opening/closingoperation of the second cutoff valve is repeated, and volume flow of agas exhausted from the second cutoff valve is calculated on the basis ofan after-filling pressure and an after-exhaust pressure of the gasfilling capacity measured by the pressure sensor, while controlling thevolume flow of the gas exhausted from the second cutoff valve bychanging the mode of the pulse shot.
 2. The pulse shot type flowcontroller according to claim 1, wherein the volume flow of the gasexhausted from the second cutoff value is calculated by calculatingvolume of the gas exhausted from the second cutoff valve every the pulseshot and integrating the volumes.
 3. The pulse shot type flow controlleraccording to claim 1, wherein the volume flow of the gas exhausted fromthe second cutoff valve is calculated on the basis of a predeterminedcycle of repeatedly making the pulse shot.
 4. The pulse shot type flowcontroller according to claim 1, wherein the mode of the pulse shot ischanged by changing the predetermined cycle of repeatedly making thepulse shot.
 5. The pulse shot type flow controller according to claim 1,wherein the mode of the pulse shot is changed by changing openingoperation duration of the first cutoff valve or the second cutoff valve.6. The pulse shot type flow controller according to claim 1, furthercomprising a temperature sensor for measuring temperature of the gasfilling capacity, wherein the volume flow of the gas exhausted from thesecond cutoff valve is calculated also on the basis of the temperatureof the gas filling volume measured by the temperature sensor.
 7. Thepulse shot type flow controller according to claim 1, wherein anafter-filling estimated pressure in a heat equilibrium state afterfilling is obtained on the basis of a change rate of pressureaccompanying an adiabatic change in a period (at the time of filling)since the opening/closing operation of the first cutoff valve isperformed until the opening/closing operation of the second cutoff valveis performed, the after-filling estimated pressure is used as theafter-filling pressure, an after-exhaust estimated pressure in a heatequilibrium state after exhaust is obtained on the basis of a changerate of pressure accompanying an adiabatic change in a period (at thetime of exhaust) since the opening/closing operation of the secondcutoff valve is performed until the opening/closing operation of thefirst cutoff valve is performed, and the after-exhaust estimatedpressure is used as the after-exhaust pressure.
 8. The pulse shot typeflow controller according to claim 1, wherein the first cutoff valve isclosed when the pressure of the gas filling capacity measured by thepressure sensor becomes a predetermined value or larger.
 9. The pulseshot type flow controller according to claim 1, wherein the controlleris used for a semiconductor manufacturing apparatus.
 10. A pulse shottype flow controlling method using a flow controller comprising: a firstcutoff valve connected to a gas source; a second cutoff valve connectedto the first cutoff valve; a gas filling capacity between the first andsecond cutoff valves; and a pressure sensor for measuring pressure inthe gas filling capacity, wherein a pulse shot of performingopening/closing operation of the first cutoff valve and, after that,performing opening/closing operation of the second cutoff valve isrepeated, and volume flow of a gas exhausted from the second cutoffvalve is calculated on the basis of an after-filling pressure/anafter-exhaust pressure of the gas filling capacity measured by thepressure sensor, while controlling the volume flow of the gas exhaustedfrom the second cutoff valve by changing the mode of the pulse shot. 11.The pulse shot type flow controlling method according to claim 10,wherein the volume flow of the gas exhausted from the second cutoffvalue is calculated by calculating volume of the gas exhausted from thesecond cutoff valve every the pulse shot and integrating the volumes.12. The pulse shot type flow controlling method according to claim 10,wherein the volume flow of the gas exhausted from the second cutoffvalve is calculated on the basis of a predetermined cycle of repeatedlymaking the pulse shot.
 13. The pulse shot type flow controlling methodaccording to claim 10, wherein the mode of the pulse shot is changed bychanging the predetermined cycle of repeatedly making the pulse shot.14. The pulse shot type flow controlling method according to claim 10,wherein the mode of the pulse shot is changed by changing openingoperation duration of the first cutoff valve or the second cutoff valve.15. The pulse shot type flow controlling method according to claim 10,further using a temperature sensor for measuring temperature of the gasfilling capacity, wherein the volume flow of the gas exhausted from thesecond cutoff valve is calculated also on the basis of the temperatureof the gas filling volume measured by the temperature sensor.
 16. Thepulse shot type flow controlling method according to claim 10, whereinan after-filling estimated pressure in a heat equilibrium state afterfilling is obtained on the basis of a change rate of pressureaccompanying an adiabatic change in a period (at the time of filling)since the opening/closing operation of the first cutoff valve isperformed until the opening/closing operation of the second cutoff valveis performed, the after-filling estimated pressure is used as theafter-filling pressure, an after-exhaust estimated pressure in a heatequilibrium state after exhaust is obtained on the basis of a changerate of pressure accompanying an adiabatic change in a period (at thetime of exhaust) since the opening/closing operation of the secondcutoff valve is performed until the opening/closing operation of thefirst cutoff valve is performed, and the after-exhaust estimatedpressure is used as the after-exhaust pressure.
 17. The pulse shot typeflow controlling method according to claim 10, wherein the first cutoffvalve is closed when the pressure of the gas filling capacity measuredby the pressure sensor becomes a predetermined value or larger.
 18. Thepulse shot type flow controlling method according to claim 10, whereinthe method is used for a semiconductor manufacturing apparatus.